This invention relates to an arc discharge preventing circuit of a transfer switch for use with an inductive load, especially suitable for a transfer switch connected in series with an electric motor for intermittently driving a wiper of a motor car.
An example of an electronic circuit arrangement adapted to decrease arc discharge of a transfer switch circuit for inductive loads is outlined in a co-pending U.S. patent application, Ser. No. 21,132, entitled "Apparatus for Preventing Arc Discharge of Transfer Switch Circuit for Inductive Load", assigned to the same applicant as the present application. The present application is directed to specific constructions of such an electronic circuit arrangement.
According to the prior art practice, for the purpose of preventing melting and fusion of switch contacts caused by arc discharge, such spark preventing means as a resistor or a capacitor has been connected across the switch contacts.
However, in an environment where the temperature condition is severe as in a car-mounted electric arrangement, the reliability of a conventional oil filled capacitor is low, and a mylar capacitor is difficult to construct so as to have a large capacitance although its capacitance variation caused by temperature variation is small, so that these capacitors are not suitable for use as an arc preventing element of a transfer switch utilized for large inductive loads.